After six seasons in Tennessee, Chris Johnson is now a free agent. The star running back has had an up-and-down career. The successes are easy to document: since 2008, only Adrian Peterson has more rushing yards, and Johnson has rushed for 1,299 more yards than the next closest back, Matt Forte. Johnson was just 32 yards shy of 10,000 yards from scrimmage with the Titans, the second most in the league over that period behind only Peterson. There was a magical 2009 season, where Johnson rushed for 2,000 yards, averaged 5.6 yards per carry, and set the still-standing record for yards from scrimmage in a season with 2,509.1

But there’s also the bad. In the four seasons since his Hall of Fame-caliber performance, Johnson has had 24 games with five or more carries where he averaged three or fewer yards per rush, the most such games in the league. In the last three seasons, Johnson has recorded 10+ carries and averaged 3.0 YPC or worse in 17 of his 48 games, also the most in the NFL. The man known as CJ2K became famous for his big play ability but has recorded a below-average YPC rate in two of the past three seasons. And while he’s never been a success rate star, he’s still checking in at below-average in percentage of successful runs in recent times, so it’s not as though the lower YPC average is a reflection of a style change to become a more consistent back. Last year, Johnson ranked 53rd in Advanced NFL Stats’ measure of success rate out of 84 eligible backs.

Johnson’s a pretty complicated back to analyze. He’s boom or bust, but he’s also displayed excellent durability over his career and is a consistent yardage machine. But he now rarely make big plays and is at an age where nothing is assured. In 2009, Johnson had 22 carries of 20+ yards; last year, he had only five such runs. So I decided a fun way to project Johnson’s 2014 season would be to run him through a similarity program based on nine factors.

Let me be clear about the methodology: my selection of statistics and weights was entirely subjective. I spent about ten minutes tinkering with the weights until I found something reasonable. No more and no less thought was put into the formula than that. The results here are not the product of rigorous analytics but rather my attempt to quantify my gut feelings. Here was how I calculated the similarity score:

Each player starts with a similarity score of 1,000. Then I subtract the absolute value of each player’s average in each metric from Johnson’s average, multiplied by a weight unique to that statistic. So the formula is 1,000 minus the sum of the following values:

The most similar back to Johnson happens to be a veteran back who switched teams just last season: Steven Jackson. Jackson’s 2012 and 2010-2012 seasons were remarkably similar to Johnson’s 2013 and 2011-2013 seasons; the two had nearly identical rushing yards and receiving yards per game over both periods; Jackson had the slightly higher yards per carry average in his most recent season, with Johnson eeking out a higher YPC average over the prior three years. The biggest difference is that Jackson was one year older than Johnson. Still, Jackson showing up as the best comp can’t be too inspiring for Johnson’s agent.

If you look at just single seasons, the similarities between Johnson’s 2013 and Jamal Anderson’s 2000 season are striking. Both were the same age, played the full season, and recorded nearly identical totals in rushing and receiving yards (although Johnson did have a small edge in YPC). Anderson recorded just 190 more yards before retiring, so this would be another scary comp.

Jackson and Anderson are just two examples, how did this group overall fare in Year N+1? Obviously we don’t know how Maurice Jones-Drew will far just yet, and Joe Morris missed the 1989 season with a broken right foot. The table below displays the results from the other 23 backs3 in Year N+1, along with a simple4 average of those players statistics:

In some ways, these results aren’t too surprising. The players are projected to play in 13.7 games, which is actually pretty good; a sample of 23 random running backs would normally be projected for fewer games, I think, and that’s even more likely when you consider that these backs are older than average. But I think the similarity scores reflect Johnson’s durability, which is a good sign.

The production is solid but not great; if we pro-rate these averages to 16 games, we come up just shy of a 1,000-yard season. That would be the worst season of Johnson’s career, but then again, older running backs can drop off steeply and randomly. This formula projects a 3.8 yards per carry average and 6 touchdowns, along with modest receiving numbers. Only two players — Delvin Williams in 1978 and Emmitt Smith in 1998 — had a yards per carry average over 4.1, although four other players had 1550+ yards from scrimmage. So it’s clear that hope isn’t lost: Johnson could still be expected to have another strong season, especially if he lands in the right situation. But for an expected result rather than an optimistic one, it’s probably best to look at median numbers, which show a projection of 16 games, 257 carries, 998 yards, a 3.81 yards per carry average, 6 touchdowns, and again very modest receiving numbers.

Frankly, these results seem pretty good. My guess is that in August, most fantasy sites will wind up with a projection in the neighborhood of 250-1000-6 for Johnson in 2014. And there’s some value to that. But the idea that any team will pay Johnson “big money” in free agency because they desire a home-run hitting back is silly. And probably more a media creation than anything, as I doubt Johnson winds up getting a very impressive contract. He’s simply not the explosive force he used to be; now he’s more grinder than anything, but one not particularly successful at that. But he can still churn out a 250-carry, 1000-yard season, and that skill is still in some demand.

Less relevant but one of my favorite Johnson moments came in the 2007 Hawaii Bowl against a Boise State team that would go 38-2 over the following three seasons. In that game, East Carolina won 41-38 as Johnson rushed for 223 yards and scored two touchdowns on 28 carries. That’s the second most rushing yards allowed by Boise State to any player since 2000. [↩]

With the three players who played in 1982 pro-rated to 16-game seasons. [↩]

Arguably the proper thing to do would be to take a weighted average, but well, I got lazy at the end and considering the fudging I did to create the formula, a simple approach is arguably more proper. [↩]